Well drilling

ABSTRACT

A method and apparatus for physically restraining a drill string at various points above the earth&#39;&#39;s surface and below the apparatus for rotating the drill string to prevent substantial lateral displacement of the drill string during rotation thereof for drilling purposes.

United States Patent 1191 McEntire Sept. 17, 1974 [5 WELL DRILLING 2,450,934 10/1948 Calhoun 175 25 x 1751 Invent R9919 M91999 P191019- 5132x123 5/1322 1 5113211111131---- IIIIIIII. 1 v i/ 5'i [73] Assignee: Atlantic Richfield Company, New 11581212 11/1964 Fanshflwe et York N Y 3,158,213 11/1964 ONeill et a1. 3,334,606 8/1967 Deal et a1. [22] Filed: Sept. 18, 1972 3.528.497 9/1970 Lehman 3,702,640 11 1972 C' t 7 8 21 Appl. 190.; 289,830 5/ 5 Primary Examiner-Frank L. Abbott [52] U.S. C1 175/65, 173/1, 175/220, Assistant Examiner-Richard E. Favreau 308/4 Attorney, Agent, or Firm-Roderick W. MacDonald [51] Int. Cl ..E21b 17/10 FlGld of Search 65, 85, 173/165, 163, 57; 308/39; 24/263 D, 263

D A 263 SC A meth od and apparatus for physlcally restraining a drill string at various points above the earths surface [56] References Cited and below the apparatus for rotating the drill string to UNITED STATES PATENTS prevent substuntiztl later-11 displacement of the drill string durmg rotatlon thereof for dr1111ng purposes. 1,772,368 8/1930 Sheldon 175/57 2,276,016 3/l942 Bruntly 175/220 X 8 Claims, 8 Drawing Figures WELL DRILLING BACKGROUND OF THE INVENTION Heretofore, various types of apparatus have been employed to rotate a drill string with a bit on the lower end thereof to drill a wellbore in the earth. Many of these types of apparatus employ above ground apparatus for rotating the drill string. Numerous devices have been employed for such a purpose, for example, the conventional rotary table which sits in the working floor of the derrick or an electric motor or power sub which is hung in the derrick above the working floor (US. Pat. No. 3,670,832, the disclosure of which is incorporated herein by reference), but with these types of apparatus there can be a substantial length of drill string which extends between the top of the wellbore at the earths surface and the drill string rotating device itself.

Depending upon the magnitude of various parameters as hereinafter set forth in detail, a drill string cannot be rotated above a certain speed without causing substantial lateral displacement or whirling of the drill string in the space between the top of the wellbore and the drill string rotating apparatus. A small amount of lateral displacement is tolerable without causing undue harm to the drilling method and apparatus. However, with some conventional drilling procedures and apparatus, and, particularly, with the less conventional slim hole procedures and apparatus (very small diameter wellbores and very high rotation rates for the drill string), substantial lateral displacement of the drill string above the wellbore cannot be tolerated. This is so because there may be some sacrifice in safety, and- /or increase in wear on the drill string and/or undesired vibration of the drill string in the wellbore. In the case of slim hole drilling, downhole vibration can be catastropic as is fully and completely disclosed in US. Pat. No. 3,635,294, the disclosure of which is incorporated herein by reference.

Substantial lateral displacement of the drill string above the top of the wellbore can occur in any of the above types of drilling apparatus, even those which employ a conventional rotary table, when the working floor of the rig is elevated a substantial distance over the surface of the earth to accommodate blowout preventers and the like. Thus, even with conventional rigs there can be a substantial length of drill string extending between the top of the wellbore and the drill string rotating apparatus and this section of drill string can, under certain conditions, be subject to undesired and harmful lateral displacement during drilling.

SUMMARY OF THE INVENTION According to this invention, harmful lateral displacement of a drill string above the top of the wellbore is essentially independent of the torque applied to that drill string and a mathematical formula is employed to define the maximum length of drill string above a wellbore that can be left substantially laterally unrestrained without causing harmful lateral displacement at any given rotation rate for the drill string.

It has been discovered that with proper lateral restraint of the drill string between the top of the wellbore and the drill string rotating apparatus, undesired vibrations of the drill string downhole in the wellbore are also reduced.

It has further been discovered that by employing the lateral restraint technique of this invention, downhole vibration of the drill string is reduced even though substantial lateral displacement of the drill string occurs above the area where the lateral restraint technique of this invention is employed. Thus, by employing this invention, a filtering effect is produced on the drill string which helps prevent downhole vibration of the drill string even though substantial lateral displacement takes place in the drill string above the area to which the lateral restraint technique of this invention is applied.

Accordingly, it is an object of this invention to provide a new and improved method and apparatus for drilling a well. It is another object to provide a new and improved method and apparatus for controlling the lateral displacement of a drill string above a wellbore. It is another object to provide a new and improved method and apparatus for reducing downhole vibration in a drill string. It is another object to provide a new and improved method and apparatus for filtering downhole vibration out of a drill string even though substantial lateral displacement of the drill string occurs above the wellbore.

Other aspects, objects and advantages of this invention will be apparent to those skilled in the art from this disclosure and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a simplified elevation view of a drilling rig and a drill string rotation apparatus useful in this invention.

FIG. 2 shows a graph of various modes of vibration that may occur in a drill string.

FIG. 3 shows a partial cross-sectional view of a restraining means useful in this invention.

FIG. 4 shows the restraining means of FIG. 3.

FIG. 5 shows a top view of another restraining means within this invention, the restraining means being in the extended position for enclosing a drill string.

FIG. 6 shows a side view of the restraining means in the extended position of FIG. 5.

FIG. 7 shows a top view of the restraining means of FIG. 5 but in the retracted position, i.e., not enclosing a drill string.

FIG. 8 shows a side view of the retracted restraining means of FIG. 7.

More specifically, FIG. 1 shows a drilling rig l sitting on the earths surface 2 over a wellbore 3 wherein the working floor 4 is raised above the earths surface by leg 5'. Working floor 4 carries a derrick 5 topped by a crown block 6 which supports by way of a plurality of cables 7 a traveling block 8. Suspended from traveling block 8 by way of cable 9 is an electric motor or power sub 10 such as that which is fully disclosed in US. Pat. No. 3,670,832. Motor 10 is attached to and rotates drill string 11 which passes through an opening in floor 4 and into wellbore 3, the lower end of drill string 1 1 (not shown) carrying a bit. which rotates when motor 10 rotates drill string 11. Sitting on floor 4 and around the opening in that floor is a rotary table 12 which has an opening 13 therein through which drill string 11 passes.

In conventional drilling, opening 13 contains a kelly bushing which receives a kelly which is connected to the drill string so that rotation of the rotary table by a diesel motor or other surface power means rotates the kelly bushing and kelly and in turn rotates the drill string and bit. Because of the use of motor 10, the kelly and kelly bushing are removed so that a substantial space 13 in the rotary table is present. Thus, the drill string in space 13 is relatively laterally unrestrained and a high rate of rotation of drill string 11 can produce a substantial lateral displacement 14 of the drill string.

This lateral displacement can be harmful in that it can cause fatigue or breakage of tool joints in the drill string as well as substantial vibration of the drill string itself both in the area between earths surface 2 and drill string rotation apparatus and downhole in wellbore 3.

According to this invention, drill string 11 is laterally restrained at at least two points between surface 2 and motor 10. If lateral restraint according to this invention is employed at two points, an effective filter means is established so that even though lateral displacement of drill string 11 takes place above the two points of lateral restraint, downhole vibration of drill string 11 is still substantially reduced.

By utilizing more than two points of restraint substantially the entire length of drill string 11 between surface 2 and motor 10 can be excluded from any harmful lateral vibration while still reducing downhole vibration of drill string 11 in wellbore 3. Because of the discovery that the maximum rotating rate for a drill string above which substantial lateral deflection occurs is essentially independent of the torque applied to the drill string, the maximum length of drill string between the top of wellbore 3, i.e., surface 2, and the drill string rotating apparatus, i.e., motor 10, which can be left laterally unrestrained when rotating at a known rate of R revolutions per minute can be determined by the formula R 30 n/L lT/p. (n 1r/L) El/p.

where:

R is the known rate of rotation of the drill string in rpm,

n is the mode of vibration to be damped as further explained with reference to FIG. 2 hereinafter,

L is the length in feet of drill string 11 that can be laterally unrestrained without substantial lateral displacement at the drill string rotation rate R,

Tis the tension load in pounds in the drill string pipe,

E is Youngs modulus in pounds per square inch for the drill string pipe,

I is the moment of inertia in (inches)" for the drill string pipe,

u is the mass in slugs per foot of drill string including the drilling fluid contained in the drill string during drilling at rotation rate R.

By employing the desired rate R in the formula and solving for length L, the maximum laterally unrestrained length for drill pipe 11 between surface 2 and motor 10 can be determined. Thereafter, physical lateral restraining of the drill string between surface 2 and motor 10 at at least two points is employed so that at least filtering out of downhole vibration in the drill string is achieved according to this invention. If desired or needed, physical lateral restraining at more than two points along the length of drill string 11 between surface 2 and motor 10 can be employed so that no part of the drill string in this area is physically unrestrained for a distance greater than about length L and all substantial lateral displacement of the string is eliminated.

Lateral restraining of the drill string should be accomplished without causing any longitudinal restraining of the string so that the string is free to move up and down (longitudinally) through the restraints during drilling.

The lateral restraint of the drill string need not prevent all lateral displacement of the string but only substantial lateral displacement which can prove harmful to the drilling method and/or apparatus. The amount of permissible lateral displacement will vary widely depending upon the particular situation. The restraint will, however, generally confine the drill string in a plane substantially normal to the longitudinal axis of the drill string to an area which has an effective largest cross-sectional dimension varying from essentially the outside diameter of the drill pipe up to not substantially greater than about two diameters of the drill string. An effective largest cross-sectional dimension means the largest cross-sectional dimension through which the drill string can travel within the confining space. If the confining space is circular, then the effective largest cross-sectional dimension is the diameter of the confining space. If the confining space is square in cross section, the effective largest cross-sectional dimension will be the largest dimension through which the drill string will pass and touch opposite parts of the confining space. Thus, in the case of a square restriction, the effective largest cross-sectional dimension will not be from one corner to the opposite comer if the pipe cannot touch the comer but rather will be from a point close to one corner to a point close to the opposite corner, the pipe actually touching these points when moving along that dimension. In other words, whether the restraint area is circular or noncircular, the effective largest cross-sectional dimension is the longest substantially horizontal dimension through which the drill pipe can physically move before touching a part of the restraint.

FIG. 2 shows three modes of vibration. The upper curve is the first mode of vibration where n in the formula equals 1. The middle curve shows the second mode of vibration where n is represented by 2. The bottom curve shows the third mode of vibration where n is represented by 3, and so on. Normally, removal of the first mode of vibration removes the remaining modes of vibration so that n in the above formula is normally 1. If, for example, it is determined that the first mode of vibration can be tolerated and that only the second, third, etc., modes need be removed, n in the formula would be represented by 2. Generally, n will vary from 1 to 5 and is preferably 1 for the reasons set forth above. There can be an unlimited number of n values but from a practical standpoint consideration need not be given to more than the first five modes of vibrations.

FlG. 3 shows a cross section of rotary table 12 of FIG. 1 with a restraining means according to this invention employed in space 13. The restraining means is composed of at least two segments, in the embodiment of FIG. 3 two semicircular segments 30 and 31, which mate together when in space 13 to provide a passage 32 through which drill string 11 can move longitudinally but which is of substantially smaller diameter than space 13 so that drill string 11 is laterally restrained. The bottom side of segment 30 has welded or otherwise fixed thereto at 33 a flange member 34. Flange 34 extends under the bottom of adjacent segment 31 so that when both segments and 31 are in place in space 13 to encompass drill string 11 in space 32, segment 31 is in contact with flange 34 of segment 30.

FIG. 4 shows segments 30 and 31 to be frusto-conical in configuration and shows that segment 31 also carries a flange means 35 which extends under the bottom side 36 of segment 30 when both segments are in place in space 13. Thus, each segment has its own flange which will be in contact with at least one other segment when all segments are in place in space 13. By employing this restraint means with its co-acting flanges all segments are held by gravity in a mutually supporting arrangement upon their first being placed in the rotary table space.

The rotary table with the restraint of this invention, as shown in FIGS. 3 and 4, can be one point of restraint for the drill string. Another point of restraint can be at the top of wellbore 3 or anywhere else below table 12 and above surface 2 and/or above table 12 and below motor 10. For example, additional restraining means can be employed in the derrick part of the rig as shown in FIG. 5 wherein a portion of the derrick 5 is shown to carry at least two curvilinear sections, two semicircular sections and 51 in FIG. 5, the sections sized to fit together as shown in FIG. 5 around and enclosing drill string 1 1. The sections in this position form an enclosure having an effective largest cross-sectional dimension which is diameter 52 as described hereinabove. Means 53 and 54 are attached to derrick 5 and to swivels 55 and 56 on sections 50 and 51, respectively for raising and lowering sections 50 and 51. Means 53 and 54 is shown to be a wire cable but can be any suitable holding means such as any type of rope, fixed rod, and the like. A pair of hydraulic cylinders 57 and 58 are also carried by derrick 5 and pistons 59 and 60 of these cylinders are attached to swivel 55. Similarly, hydraulic cylinders 61 and 62 are attached to derrick 5 and their pistons 63 and 64 are attached to swivel 56. Any functionally equivalent mechanical means can be substituted for the hydraulic cylinders and pistons shown in FIGS. 5-8.

FIG. 6 shows a side view of the restraining apparatus of FIG. 5 in the extended, i.e., drill string enclosing, position.

FIG. 7 shows the apparatus of FIG. 5 in a retracted position wherein the apparatus is not in use as a restraining means for drill string 11 while FIG. 8 shows a side view of the apparatus in its retracted position of FIG. 7.

In operation, for extending the apparatus of FIG. 8 from the retracted position to the enclosing position of FIGS. 5 and 6, cables 53 and 54 are used to draw the sections upwardly to the desired position relative to drill string 11 after which pistons 60 and 63 of inner cylinders 58 and 61 are extended to the desired distance and finally pistons 64 and 59 of cylinders 62 and 57 are extended to bring sections 50 and 51 into their enclosing position around drill string 11 as shown in FIG. 5. The above sequence of operations is reversed to move the apparatus from its enclosing position to its retracted position of FIGS. 7 and 8.

The apparatus of FIGS. 3 and 4 and the apparatus of FIGS. 5 through 8 can be used in conjunction with on another on the same drill string as can other suitable restraining means be used on the same or different drill string to achieve the advantages of this invention.

As an example, employing the concept of this invention in a slim hole drilling system, using 2 inch outside diameter (1.815 inch inside diameter) drill string pipe having a Youngs modulus of 30 X 10 psi and a moment of inertia of 1.029 inch, and a drill string p. of 0.24 slug per foot when using a ten pound per gallon drilling fluid, and employing 10,000 pound tension in the drill string pipe, the length L calculates to be 8 feet so that the drill string between the surface of the earth and the drill string rotating apparatus should be constrained from substantial horizontal movement at intervals no longer than eight feet for rotation speeds of the drill string up to 1,500 rpm to avoid all modes of vibration (n 1).

Alternatively, means 53 and 54 can be of fixed length so that only the hydraulic cylinders are actuated to accomplish the desired enclosing and retracting operations shown in FIGS. 5-8. In this alternate for extending to the enclosing position inner cylinders 58 and 61 are actuated to extend their pistons first after which the outer cylinders 57 and 62 are actuated to extend their pistons and bring sections 50 and 51 into enclosing engagement with the drill string. This sequence of steps is then reversed to retract the sections 50 and 51 from enclosing engagement with the drill string.

Reasonable variations and modifications are possible within the scope of this disclosure without departing from the spirit and scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a drilling method wherein a drill string carrying a bit on its lower end is rotated at a known rate in a wellbore and a part of the drill string extends from the top of the wellbore to the apparatus which rotates the drill string, the improvement comprising determining the maximum length of the drill string that can be unrestrained above the wellbore without substantially laterally displacing the drill string when rotating same at said known rate, said determination step being made following the formula where:

R is said known rate in rpm,

n is the mode of vibration to be damped,

L is the length in feet of drill string that can be laterally unrestrained without substantial lateral displacement at said rate R,

T is the tension load in pounds in the drill string pipe,

E is Youngs modulus in psi for the drill string pipe,

I is the moment of inertia in (inches) for the drill string pipe, and [L is the mass in slugs per foot of drill string including the drilling fluid contained in said drill string, physically laterally restraining said drill string at at least two points not substantially further apart along the length of said drill string than about the distance L in the above formula, said lateral restraining being in the area from near the top of said wellbore to near said drill string rotation apparatus, and allowing said drill string to move longitudinally notwithstanding said lateral restraint.

2. A method according to claim 1 wherein n is from 1 to 5.

3. A method according to claim 1 wherein n is l.

4. A method according to claim 1 wherein each lateral restraint of said drill string employs a confining space which in a plane substantially normal to the longitudinal axis of said drill string has an effective largest cross-sectional dimension not substantially greater than about two diameters of said drill string.

5. Apparatus for laterally restraining a rotating drill string passing through a rotary table comprising a wear bushing adapted to fit into the space of said rotary table through which said drill string passes, said bushing being composed of at least two separate frusto-conical segments which fit together in said space in said rotary table to encompass said drill string and to reduce the lateral distance said drill string must travel in said space in said rotary table before encountering a restraint, each segment having fixed on a lower portion thereof a flange means, the flange means of one segment overlapping the lower side of at least one other segment so that when all segments are emplaced in said space in said rotary table each segment rests on a flange means from at least one other segment.

6. Apparatus for laterally restraining a drill string in a rotary drilling rig which has a floor and an upstanding derrick means that supports said drill string, said apparatus comprising at least two curvilinear sections sized to fit together around and enclose said drill string at a point intermediate said floor and the top of said derrick means, means carried by said rig and fixed to said sections for moving said sections (1) together around said drill string and (2) apart and away from said drill string and toward a part of said derrick, each section being fixed to at least two hydraulic means for moving said sections together around said drill string and away from said drill string, and means for moving each section with its attached hydraulic means toward and away from said drill string.

7. Apparatus according to claim 6 wherein there are two semicircular sections, each section is fixed to two hydraulic means, and each section and its associated hydraulic means is attached to a cable means for raising and lowering said sections.

8. Apparatus for laterally restraining a rotating drill string passing through a rotary table of a drilling rig comprising a wear bushing adapted to fit into the space of said rotary table through which said drill string passes, said bushing being composed of at least two separate frusto-conical segments which fit together in said space in said rotary table to encompass said drill string and to reduce the lateral distance said drill string must travel in said space in said rotary table before encountering a restraint, each segment having fixed on a lower portion thereof a flange means, the flange means of one segment overlapping the lower side of at least one other segment so that when all segments are emplaced in said space in said rotary table each segment rests on a flange means from at least one other segment, separate from said bushing at least two curvilinear sections sized to fit together around and enclose said drill string, and means carried by said rig and fixed to said sections for moving said sections together around said drill string and away from said drill string. 

1. In a drilling method wherein a drill string carrying a bit on its lower end is rotated at a known rate in a wellbore and a part of the drill string extends from the top of the wellbore to the apparatus which rotates the drill string, the improvement comprising determining the maximum length of the drill string that can be unrestrained above the wellbore without substantially laterally displacing the drill string when rotating same at said known rate, said determination step being made following the formula R 30 n/L square root T/ Mu + (n pi /L)2 EI/ Mu where: R is said known rate in rpm, n is the mode of vibration to be damped, L is the length in feet of drill string that can be laterally unrestrained without substantial lateral displacement at said rate R, T is the tension load in pounds in the drill string pipe, E is Young''s modulus in psi for the drill string pipe, I is the moment of inertia in (inches)4 for the drill string pipe, and Mu is the mass in slugs per foot of drill string including the drilling fluid contained in said drill string, physically laterally restraining said drill string at at least two points not substantially further apart along the length of said drill string than about the distance L in the above formula, said lateral restraining being in the area from near the top of said wellbore to near said drill string rotation apparatus, and allowing said drill string to move longitudinally notwithstanding said lateral restraint.
 2. A method according to claim 1 wherein n is from 1 to
 5. 3. A method according to claim 1 wherein n is
 1. 4. A method according to claim 1 wherein each lateral restraint of said drill string employs a confining space which in a plane substantially normal to the longitudinal axis of said drill string has an effective largest cross-sectional dimension not substantially greater than about two diameters of said drill string.
 5. Apparatus for laterally restraining a rotating drill string passing through a rotary table comprising a wear bushing adapted to fit into the space of said rotary table through which said drill string passes, said bushing being composed of at least two separate frusto-conical segments which fit together in said space in said rotary table to encompass said drill string and to reduce the lateral distance said drill string must travel in said space in said rotary table before encountering a restraint, each segment having fixed on a lower portion thereof a flange means, the flange means of one segment overlapping the lower side of at least one other segment so that when all segments are emplaced in said space in said rotary table each segment rests on a flange means from at least one other segment.
 6. Apparatus for laterally restraining a drill string in a rotary drilling rig which has a floor and an upstanding derrick means that supports said drill string, said apparatus comprising at least two curvilinear sections sized to fit together around and enclose said drill string at a point intermediate said floor and the top of said derrick means, means carried by said rig and fixed to said sections for moving said sections (1) together around said drill string and (2) apart and away from said drill string and toward a part of said derrick, each section being fixed to at least two hydraulic means for moving said sections together around said drill string and away from said drill string, and means for moving each section with its attached hydraulic means toward and away from said drill string.
 7. Apparatus according to claim 6 wherein there are two semicircular sections, each section is fixed to two hydraulic means, and each section and its associated hydraulic means is attached to a cable means for raising and lowering said sections.
 8. Apparatus for laterally restraining a rotating drill string passing through a rotary table of a drilling rig comprising a wear bushing adapted to fit into the space of said rotary table through which said drill string passes, said bushing being composed Of at least two separate frusto-conical segments which fit together in said space in said rotary table to encompass said drill string and to reduce the lateral distance said drill string must travel in said space in said rotary table before encountering a restraint, each segment having fixed on a lower portion thereof a flange means, the flange means of one segment overlapping the lower side of at least one other segment so that when all segments are emplaced in said space in said rotary table each segment rests on a flange means from at least one other segment, separate from said bushing at least two curvilinear sections sized to fit together around and enclose said drill string, and means carried by said rig and fixed to said sections for moving said sections together around said drill string and away from said drill string. 